the fm modulator doesn't allow local fm stations to bleed in and disprupt the signal from the sirius/xm or even an ipod. It's about 30 bucks at bestbuy and simple to install yourself. If you can get to the part of yuour car stereo where the antennae plugs in, you can install it. Then you have an 1/8" input for anything, and local radio stations don't interfere.
In 2003, the fcc forced both sirious and xm to reduce the fm output from their radios. Since then, even with the 'booster' fm transmitter antennae included with the car kit, local fm stations do interfere and bleed into the signal from the sirous/xm radio in the car.
Poor reception in wooded areas is a blockage to the north, thats where the satelittes reside, actually over wisconson. The newer radios have a bigger buffer memory to deal with that. The factory installed radios and antennaes do proivide better sound.
i have both sirius and xm as well, 2 of each. My favorite radio is my stilletto, i use it everywhere.
I threw the headphones that came with it away(except for the plug), and made an antennae from the plug from the headphones, and just use earbuds when i carry it out on the lake or something.
Incidently, if one has directtv or dish network, and wants to install a home sirius/xm radio, one of the best places to mount the sirius/xm antennae is on the back of the dish. If you get a l bracket, and screw it on to the part of the dish where the azmith adjustment is, the sirius/xm antennae picks up really well stuck to the top of that 'new bracket'.
I have a buddy that has a car stereo shop and help him out on a regular basis. That's where I learned about installing sirius/xm radios
I would cancel the xm, as the merger really has put most everything i like on sirius with the 'best of xm' package, but i bought lifetime subscriptions for both xm and sirius a long time ago.